Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $202.31   3.319%   $209.0247   $209.02   $209.00   $209.00  
  Purchase #2 $56.69   11.157%   $63.0149   $63.01   $63.00   $63.00  
  Purchase #3 $234.28   11.480%   $261.1753   $261.18   $261.20   $261.20  
  Purchase #4 $112.78   6.465%   $120.0712   $120.07   $120.05   $120.10  
  Purchase #5 $100.28   12.591%   $112.9063   $112.91   $112.90   $112.90  
  Purchase #6 $113.77   9.690%   $124.7943   $124.79   $124.80   $124.80  
  Purchase #7 $126.70   7.416%   $136.0961   $136.10   $136.10   $136.10  
  7 purchase totals = $946.81       $1,027.0828   $1,027.08   $1,027.05   $1,027.10